Traditionally, most commercially available inkjet printers have a print engine which forms part of the overall structure and design of the printer. The body of the printer unit is typically constructed to accommodate the printhead and associated media delivery mechanisms, and these features are integral with the printer unit.
This is especially the case with inkjet printers that employ a printhead that traverses back and forth across the media as the media progresses through the printer unit in small iterations. Typically, the reciprocating printhead is mounted to the body of the printer unit such that it can traverse the width of the printer unit between a media input roller and a media output roller, with the media input and output rollers forming part of the structure of the printer unit. It may be possible to remove the printhead for replacement, however the other parts of the print engine, such as the media transport rollers, control circuitry and maintenance stations, are usually fixed within the printer. Replacement of these parts is not possible without replacement of the entire printer.
As well as being rather fixed in their design construction, printers employing reciprocating type printheads are relatively slow, particularly when performing print jobs of full colour and/or photo quality. This is due to the fact that the printhead must continually scan the stationary media to deposit the ink on the surface of the media and it may take a number of swathes of the printhead to deposit one line of the image.
Recently, ‘pagewidth’ printheads have been developed that extend the entire width of the print media. The printhead remains stationary as the media is transported past its array of nozzles. This increases print speeds as the printhead no longer needs to perform a number of swathes to deposit a line of an image. Instead, the printhead deposits the ink on the media as it moves past at high speeds. With these printheads, full colour 1600 dpi printing at speeds of around 60 pages per minute are possible. Such speeds were unattainable with conventional inkjet printers.
High print speeds require high precision and high speed paper movement, and as such, the entire print engine (printhead, paper handling mechanisms and control circuitry etc) must be configured accordingly to ensure high quality output.
Accordingly, there is a need to provide a print engine having a pagewidth printhead that can be readily employed within a printer body for consistent, high speed printing.
Unfortunately, individual nozzles on a printhead will malfunction through clogging, air bubbles in the ink, fabrication errors and so on. Obviously, this is detrimental to print quality. It is possible to combat this with dead nozzle compensation in the print engine controller (PEC) and nozzle redundancy (surplus nozzles) on the printhead. However, eventually too many nozzles will fail for these mechanisms to work, and the print quality is compromised. By providing the printhead in a replaceable printhead cartridge, the printhead can be replaced when the print quality deteriorates, rather than replacing the entire printer.
A pagewidth printhead needs to be precisely mounted relative to the paper path and the nozzles need to receive data and power from the printer. Furthermore, most printheads have a maintenance station to seal and clean the nozzles when not in use. This also requires power from the printer. Providing electrical power for to the cartridge for the maintenance station would be relatively easy but the cartridge would need to have the motors or other actuators that drive the cleaning and capping operations. Putting motors in a replaceable cartridge significantly increases the unit cost. As the cartridge is a ‘consumable’, it is preferable to provide the cartridge with mechanical power instead of electrical. This minimizes the mechanisms that the cartridge needs to carry and therefore reduces costs. However, establishing a mechanical coupling between the cartridge and the printer is more difficult than an electrical connection. Making these various connections every time a printhead cartridge is replaced would typically require a fairly involved cartridge replacement procedure and or a complex cartridge cradle in the printer. This has disadvantages for both the end user and the manufacturer.